In process measurements technology, for example, in chemical, biotechnological, pharmaceutical and food technical processes, and in environmental technology, automatic analytical devices or analyzers are frequently used for determining a measured variable of a liquid sample. For example, analytical devices can be applied for monitoring and optimizing the cleaning effectiveness of a clarification plant, for monitoring drinking water or for quality monitoring of food. Measured and monitored is, for example, the content in the liquid sample of a certain substance, which is also referred to as the analyte. Analytes can be, for example, ions, such as ammonium, phosphate, silicate or nitrate, biological or biochemical compounds, e.g. hormones, or even microorganisms. Other measured variables, which are determined by analytical devices in process measurements technology, especially in the field of monitoring water, include total carbon content (TOC) and chemical oxygen demand (COD). Analytical devices can be embodied, for example, as cabinet devices or as buoys.
Frequently in analytical devices, the sample to be analyzed is treated by mixing with one or more reagents, so that a chemical reaction can occur in the liquid sample. Preferably, the reagents are so selected that the chemical reaction is detectable by means of physical methods, for example, by optical measurements, by means of potentiometric or amperometric sensors or by measuring conductivity. For example, the chemical reaction can bring about a coloring or a color change, which is detectable with optical means. The color intensity is, in this case, a measure for the measured variable to be determined. The measured variable can be ascertained, for example, photometrically, in that electromagnetic radiation, for example, visible light, is radiated from a radiation source into the liquid sample and after transmission through the liquid sample is received by a suitable receiver. The receiver produces a measurement signal dependent on the intensity of the received radiation, from which the measured variable can be derived.
In order to use such analytical methods in an automated fashion, for example, for industrial applications or for monitoring a clarification plant or a body of water in the outdoors, it is desirable to provide an analytical device, which performs the required analytical method in an automated fashion. The most important requirements for such an analytical device are, besides a sufficient accuracy of measurement, robustness, simple serviceability and the assurance of a sufficient working-, and environmental safety.
Semiautomatic and automatic analytical devices are known from the state of the art. Thus, for example, DE 102 22 822 A1, DE 102 20 829 A1 and DE 10 2009 029305 A1 disclose online-analyzers for analyzing samples. These online-analyzers are embodied, in each case, as cabinet devices, which include a control unit, supply containers for reagents, standard solutions and cleaning liquids, pumps for transporting and dosing liquid samples, and the one or more reagents, into measuring cell, and measuring transducers for optical measurements on the liquid sample treated with the one or more reagents in the measuring cell. The reagents, standard solutions or cleaning liquids are transported from the supply containers and into the measuring cell. Used liquid is transferred from the measuring cell into a waste container.
In a large number of applications of such analytical devices, especially in the environmental field, the liquids to be analyzed, or monitored, can have a certain solids fraction, which can be noticed, for example, as turbidity. The solids fraction can, in the case of analytical methods, which include optical measurements as above described, lead to a corruption of the analytical result or even make measuring impossible. For example, a large amount of particles in the liquid can lead to the result that a coloring of the liquid sample is no longer detectable. The liquid is therefore frequently filtered before performing the actual analytical method. From the filtrate then a predetermined sample amount is fed into the processing unit of the analytical device and there treated and analyzed in the above described manner.
From time to time, a cleaning of the filter is required, since the particles contained in the liquid can plug the filter. Additionally, there is, for example, in the case of environmental technology and biotechnological applications, the danger that microorganisms, for example, bacteria, algae or fungi, can be held tightly in the filter and spread on the filter substrate and into its pores and, finally, likewise lessen flow through the filter.